Composite color photography



Nov. 24, 1964 P. VLAHOS 3,158,477

COMPOSITE COLOR PHOTOGRAPHY Filed April 2, 1959 2 Sheets-Sheet 1 1 {meme Mask.

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COMPOSITE COLOR PHOTOGRAPHY F iledApril 2, 1959 2 Sheets-Sheet 2 r. v BY United States Patent 3,153,477 QZGMPQSHTE ()QLQR FHQTvGl-TAPHY Petra Vlahos, Los Angeles, Calif., assignor to Motion Picture 1" search Council, The, Los Angcles, Calif, a corporation of Qalifornia ll ilcrl Apr. 2, i959, Ser. No. 8%,?67 l9 tllaims. (Qt. s d-55) This invention has to do with composite color photography, wherein a foreground scene and a background scene are separately photographed and are combined together by laboratory processes to produce a final composite picture. The invention is particularly important in the art of motion picture photography, but may also be used for still photography.

The invention has to do more particularly with the type of composite photography in which a traveling matte or mask is employed in combining the foreground and background portions of the finished picture to limit them to substantially mutually exclusive areas. The basic principles of the traveling matte process are Well. understood in the art, and many detailed procedures have been described for producing and using a traveling matte in the production of composite color photographs.

Many of those prior art composite color processes have the serious disadvantage that they are incapable of reproducing correctly foreground objects of a partially transparent nature. The process of the present invention is capable of reproducing satisfactorily all manner of transparent and semi-transparent materials, such, for example, as glassware, cigarette smoke, and blowing hair, as well as blurred edges of rapidly moving and out of focus objects.

Many processes of the prior art have the disadvantage of requiring special lighting equipment for producing illumination in non-visible spectral regions, or for producing substantially monochromatic light within the visible spectrum. That is particularly true of those prior art processes that are capable of reproducing transparent objects. The present process requires no special light sources of that type. Foreground subjects are photographed against a backing which is eifectively illuminated with light confined to a selected definite but appreciable portion of the visible spectrum. That backing illumination is typically a deep and pure blue, such as is used in the so-called blue screen processes of the prior art. Such light may readily be obtained from conventional light sources with inexpensive filters. The backing may comprise a blue-painted screen or translucent blue material that is irradiated from behind. Such backing acts as its own filter and may be irradiated with white light. When the backing is painted. with the selected color and illuminated by the same light that is used for the foreground action itself, the backing can conveniently be brought forward under the feet of an actor, or used to block out any portion of the foreground. With any of those illustrative arrangements, the backing may be considered to be illuminated with the selected color.

A further disadvantage which is common to many prior art traveling matte processes for color photography is the necessity for exposing simultaneously suitable color film for recording the foreground subject and a supplementary film for use in preparing the traveling matte. For that purpose special cameras or other optical equipmerit are required. Such equipment is usually relatively expensive, cumbersome and heavy. Moreover, special cameras are not always available, particularly for handling film of larger than standard Width, as is required for many present day wide screen processes. The present traveling matte color system has the great advantage that any camera may be used and that only a single color negative is required in the camera.

The present system is believed unique in its ability to avoid simultaneously all of the potential disadvantages just mentioned.

On the other hand, the process of the present invention is subject to a characteristic limitation which does not involve any serious practical difliculties, but must be kept in mind if fully satisfactory results are to be obtained. The process is not capable of reproducing correctly brilliant and pure colors which correspond closely to the color selected for illumination of the backing. For example, if the backing is deep blue, brilliant blues and violets should be avoided in the foreground or action material.

However, an important and novel advantage of the invention is that the limitation just described applies only to relatively deep and pure colors. Pastel shades and many colors that comprise mixtures of the backing illumination and other Wavelengths can be reproduced satisfactorily. Thus, for example, with a blue backing the present process can readily handle action that includes pastel blues, such as occur frequently in eyes and in costumes. Moreover, colors such as turquoise, which contains substantially equal parts of blue and green, may be used freely, and frequently provide much the same visual effect as pure blue.

The invention relates especially to, and Will be initially described with respect to, photographic processes in which distinct color separation records are prepared, each of which represents a particular color component of the subject matter being photographed. The color separation records are ordinarily made on black and white film and correspond to substantially mutually ex elusive Wavelength regions of the visible spectrum, typified by the three primary colors, red, green and blue. Those spectral regions typically correspond approximately to the wavelength interval from 400 to 560 millimicrons for blue, from 500 to 600 millimicrons for green, and from 600 to 700 millimicrons for red. It will be understood, however, that the invention in its broader aspects is not limited to any particular selection of primary colors, nor to the use of just three distinct spectral regions.

For clarity and consistency, the several separation records, Whether positive or negative, Will be designated by the color of the light received from the original subject. Thus, the blue record carries the information regarding blue light received from the subject photographed.

P When such color separation records are employed in a composite photographic process, one set of color separation records is ordinarily prepared for the background scene and another set for the foreground or action portion of the picture. The background and the action separation records are then combined to produce the complete picture. In one illustrative procedure, the background and action separation records for each wavelength region are first combined to produce a set of color separation records for the complete picture; and, finally, those complete color separation records are printed by areas-7v 9 all any desired color process to form the final color picture. Alternatively, the background and the action color separation records may be combined directly to produce a complete color picture, usually a color negative from which release positives may be printed as required.

In combining the background and the action color separation records for each wavelength region, two complementary procedures are available in principle. Action and background records may be printed successively to produce a composite record, each initial record being effectively opaque, or rendered opaque by suitable masking, in the picture area of the other. Alternatively, action and background records may be printed in superposition, each record then being clear in the picture area of the other. Some of the advantages of the present invention are obtainable with either type of procedure. However, only the first mentioned procedure, utilizing successive printing exposures, provides the flexibility that is desirable for maintaining correct color balance between the action and background portions of the picture. Moreover, only by using positive rather than negative records for producing the composite are semi-transparent objects realistically eproduced. Since a primary advantage of the present invention is its ability to reproduce transparent action material, it is ordinarily preferred to employ positive rather than negative records and to expose successively rather than in superposition for the step of combining action and background scenes. For clarity of description, the invention will be explained with reference to such an illustrative process.

Each positive background color separation record is typically printed through a background or male matte, which is effectively opaque in areas occupied by the action and effectively transparent in areas not so occupie Where the action involves partially transparent objects the background matte must have a density that cuts out only an appropriate amount of light from the background record.

In printing each positive action color separation record, the background area of the picture is best protected by employing an action record in which the background area is inherently effectively opaque. Such a positive record, eifectively carrying its own mask, results, for example, when the action is photographed against an eifectively black backing. The positive action separation record for each wavelength region has a dense surround if the backing illumination contains no light in that wavelength region. For example, when the backing .is pure blue, the red and green separation positives typically have substantially opaque surrounds, and require no mask, or only a light cover mask, when printed successively with the corresponding masked separation record for the background scene. That property of the red and green action positives is utilized in most of the so-called blue screen processes of the prior art.

However, in previous blue screen proces es the positive blue separation record of the action necessarily has a surround of light density, corresponding to the bright backing as seen in blue light. To combine such a positive action record with the corresponding blue background record, it must be provided with a dense mask, known as the female or action matte, which is effectively clear in the action area of the picture and opaque in the background area.

An action matte of that type can be prepared readily enough in principle, as by making a high density, high contrast photographic negative of the background matte, already described. However, it is very difiicult in practice, if not impossible, to obtain perfect register or correspondence between the working edges of such action and background mattes. Any departure of those edges from a strictly complementary relation leads to a blue or a minusblue line at the action boundary in the finished picture.

Moreover, use of a dense action matte with one of the action separation records tends to destroy the color balance of any partially transparent objects in the action. For example, if the blue action record must be so masked, the blue component of a transparent object is typically eliminate from the finished picture. That is particularly objectionable in the rendition of smoke.

T he present invention completely avoids the use of a dense action matte, even for printing the separation record for the wavelength region in whicn the backing is bright.

That feature of the invention is accomplished by replacing the action separation record for the wavelength region of the backing illumination by the combination of the action separation record for another wavelength region and a special compensating mask which compensates for major differences between those two records. The compensating mask, which will be referred to as the color difference mask, may be prepared from the original color record of the action, for example in a manner to be illustratively described.

in a blue screen process, for example, embodying the present invention, tne blue positive separation action record is typically replaced by the combination of the green positive separation record and a color difference mask that compensates for the major differences in density between the action portions of the blue record that is being replaced and the substituted green record. The combina tion of substitute (green) separation record and color difference mask may be consider-ed as comprising a synthetic blue separation rccor That synthetic blue separation record is then used in place of the conventional blue action separation record for supplying the blue component of the action to the composite color picture.

In preparing the color difference mask, full compensation is not made for the dilferences in density between the two color separation records, that is, between the separation record that would normally be used to represent the color illuminating the backing and the substitute separation record. If that were done, the combination of the substitute separation record and the color difference mask would be efiectively identical with the backing color separation record it is intended to replace, and nothing would be gained by the substitution. In particular, the area surrounding the action would be clear, and a dense action matte would be required, with the described disadvantages characteristic of the prior art.

instead, the color difference mask typically makes full compensation only for those colors for which the light content in the wavelength region of the backing illumination is less than a selected fraction of the light content in the wavelength region of the substitute separation record. That critical fraction, as will become clear, may be considered to provide a measure of the ability of the system to reproduce colors that approach the backing illumination in hue. It will be referred to herein as the color recognition ratio of the color difference mask.

For example, when the backing illumination is blue and the green separation is to be substituted, the color difference mask typically compensates substantially completely for all colors for which the ratio of the blue content to the green content is less than the selected color recognition ratio. Colors for which the ratio of blue to green content exceeds only slightly the selected color recognition ratio are typically partially corrected. And colors closer in hue to the backing illumination, for which the ratio of blue to green content is very large, are corrected substantially not at all.

Stated in another way, the superposed positive green separation record and color difference mask have essentially the same relative density variations as the positive blue separation record in all areas of the action for which the ratio of blue to green light is less than the selected color recognition ratio; have progressively more density than the blue separation record, and hence represent lower light intensity, as the ratio of blue to green light exceeds that selected value; and tend to approach the density of the green record in regions where blue light heavily predominates over green. The latter condition is true of the blue backing. Hence the substitute combination presents the action itself with density variations corresponding essentially to those of a blue separation record, but with the virtually opaque surround that is characteristic of the positive green record. The substitute combination for the action scene can therefore be combined with the background blue separation record by the same techniques that are regularly used for the green and red components of the picture, which do not require a dense action matte.

In describing and claiming the invention the substitute separation record and the color difference mask will usually be referred to as distinct components which are superposed to produce a substitute or synthetic separation record for the wavelength region of the backing illumination. It will be understood, however, that the densities characteristic of the substitute color separation record and the color difference mask do not necessarily appear on separate films, but can alternatively be produced in a single emulsion, as by successive exposures.

Those exposures may, for example, correspond directly to the exposures that would be employed to produce the respective density components. Accordingly, separate enumeration of such density components does not imply that they necessarily involve separate emulsions.

The invention relates also to color processes that do not ordinarily employ separate black-and-white color separation records for the several color components of the picture. For example, the action and background scenes can be photographed on color film, such as the well known color film manufactured by Eastman Kodak Company, which on development yields a color negative. When composite photography is not involved, that color negative can be printed directly to a final color positive. When composite processing or other laboratory operations such as fades and dissolves are required, the original color negative can be printed to a special color intermediate film, yielding an intermediate color positive. Printing of that color positive to the same type of intermediate film yields a color negative, generally referred to as the color dupe negative, from which release color prints may be directly printed. Since procedures of that type are widely used for printing ordinary scenes," it is useful to provide a process for composite photography that utilizes the same procedures so far as possible. The present invention provides such a process.

In accordance with one illustrative embodiment of that aspect of the invention, an intermediate color positive of the action scene is prepared which has a dense black surround and which carries information on all color components or the action except that correspond ing to the background illumination. A separate record is prepared carrying the latter information and also having a dense black surround. That dense surround is obtained, however, without use of a dense female matte. For the background scene a full intermediate color positive is printed directly from the background color negative. That background color positive is then masked with a dense male matte and printed to the dupe color negative, and the action information is printed to the same dupe color negative from the intermediate action color records already described. Release color prints may then be made directly from the complete dupe negative.

In preparation of the action intermediate color records, the color components corresponding to wavelength regions other than that of the backing illumination are typically printed directly from the action color negative by white light from which the wavelength region of the backing illumination has been removed by a suitable filter. The color component of the backing illumination is recorded in the form of a combination of substitute color separation record and color difference mask, typically identical with those already described. As in the previously described form of the invention, the substitute color separation record and color difference mask may be combined on a single piece of film.

in its broader aspects the basic principles of the invention may be employed in connection with backing illumination in the wavelength region of any one of the color separation records; and may employ as a substitute record any other color separation record in combination with a suitable color correcting mask. The advantages and limitations of any particular selection of backing illumination on substitute wavelength region, which will depend in a definite manner upon the color and other characteristics of the action material, can be determined in each instance in the light of the present disclosure.

The invention has been found to be eifective with a particularly wide and useful range of action material when the backing illumination is deep blue and when the green separation record is selected as substitute. For that reason and for the sake of clarity of explanation, and without implying any limitation upon the scope of the invention, it will be described primarily with relation to that prefered arrangement, which will be referred to for convenience as the blue screen form the invention.

An important feature of the invention is the ease with which it is possible to vary the value of the color recognition ratio, defined above. For the blue screen form of the invention, that ratio may be identified more specifically as the blue to green recognition ratio. For many scenes 2. value equal to or slightly greaterthan unity has been found to be most satisfactory. The process then provides correct color rendition of all foreground objects for which the blue light component is equal to or less than the green light component. At the same time, transparent objects of all ordinary types are well reproduced. In spite of the large amount of blue light that is transmitted through such objects from the blue backing and that would appear in a blue separation record, the substitute combination of gree separation record and color difference mask represents only the green light actually rellected from the transparent object and a limited additional amount of light due to action of the color difference mask. That additional light is limited to an amount that is determined by the green light content. Because of that action of the difference mask, the colors of transparent objects may be represented in the finished picture with somewhat more blue than they actually contain; but that added blue is limited approximately to the actual green content multiplied by the selected recognition ratio.

In a scene that contains transparent objects of particular importance, the color of such objects can be preserved more completely by processing the film for that scene with a color diiference mask for which the color recognition ratio is unity or slightly less than unity. And if the foreground must for some reason contain objects of abnormally high blue content, such colors can be reproduced more effectively by employing a color diiference mask with recognition ratio considerably larger than unity, for example 1.5 or more. Selection of a color recognition ratio to favor either opaque objects of unusually deep blue or transparent objects of special importance tends to reduce the accuracy of color rendition of the other type of such special subject matter. That, however, is not a serious practical disadvantage, since the simultaneous presence or" those special types of subject matter in the same composite scene can be avoided, and the processing procedure can be shifted conveniently to favor one or the other when it occurs alone. An intermediate value of the color recognition ratio, typically somewhat greater than unity, is capable of reproducing an adequate range of colors for ordinary purposes and of handling most transparent objects and unsharp edges highly satisfactorily.

An important practical advantage of the invention re sults from the fact that white light, regardless of its arsaarv brightness, contains definite proportions of any selected set of primary colors. For that reason all grey scale objects typically produce color separation records having identical density variations. Hence, insofar as a scene contains only grey scale objects, one color eparation rccord may be freely substituted for another in making the final color picture. Appropriate adjustment of contrast may be required, but since the several color separation records contain basically the same grey scale information, substitution of one for another does not require any detailed compensation such as has been described as the function of the color difference mask. It therefore turns out that the color difference mask has typically a definite uniform density for all grey scale objects, regardless of their brightness. That definite density Will be referred to as the grey scale density. The value of the grey scale density may in some respects be selected arbitrarily, since a higher or lower overall density level of the color difference mask can be produced by varying the printing exposure employed to produce it; and can be compensated when the mask is used by adjusting the printing exposure during printing through the substitute combination of green record and difference mask.

For reasons that will appear, there is a definite relation between the grey scale density of the color difference mask and the color recognition ratio of that mask, as defined above. Hence a desired value of the recognition ratio may be obtained by making the color difference mask with a suitably selected grey scale density.

The color difference mask has the above defined grey scale density not only for white, grey and black objects, but also for objects having colors of certain types. Colors of one such type have substantially zero light content both in the wavelength region of the backing illumination and in that of the substitute separation record. In the blue screen form of the invention, with blue backing and with green separation record as substitute, ed is such a color. For all red objects, regardless of their brightness, the correct density of the color difference mask equals substantially the grey scale density.

A second group of such colors includes those with equal light contents in the wavelength regions or" the backing illumination and of the substitute record. With the blue screen process, such colors include, for example, turquoise, which consists of substantially equal parts of blue and green; and normal flesh tones, which comprise substantially equal and relatively small amounts of blue and green in combination with red. For colors of that group also, the density of the color difference mask is essential equal to the grey scale density. It is particularly advantageous that flesh tones require little or no corrective action by the color difference mask.

The colors for which the backing and the substitute color separation records have distinctly different densities fall into two main groups. For one of those color groups, the density of the substitute record is l as than that of the backing record, so that the color difference mask must effectively increase the density of the positive green record. For such colors the color difference mask must have a density in excess of the grey scale density. In the described blue screen form of the invention, such colors include orange, yellow and, of course, green, for which the blue content is less than the green content. Colors of that type will be referred to for convenience as blue-deficient colors.

The other group of colors requiring correction, which will be referred to as blue-excess colors, contain more blue than green. For correct reproduction of blue-excess colors, the color difference mask must increase the relative brightness, and hence reduce the relative density, of the positive green separation record. Such action results if the density of the color difference mask for those colors is less than the grey scale density. The degree to which correction of that type can be effected by the color difference mask is definitely and automatically limited by the value sel cted for the grey scale density. The maximum effective reduction of density of the green separation record for any color occurs when the mask is clear, and is equal to the grey scale density. Greater effective density reduction, for given grey scale density, would require presence of a negative density.

For usual aotlion material it is useful to provide a grey scale density slightly higher than the clear film, so that colors that are slightly blue-excess will be recognized by the process as being distinct from white. That statenent is equivalent to the criterion already specified above, that for usual action material a satisfactory value of the blue recognition ratio is slightly greater than unity.

A full understanding of the invention, and of its further objects and advantages, will be had from the following description of certain illustrative manners of carrying it out, of which description the accompanying drawings form a part. The particulars of that description are intended for illustration only and not as a limitation pen the scope of the invention, which is defined in the appended claims.

in the drawings:

FIG. 1 is a schematic drawing representing illustrative procedure in accordance with the invention for photogra hing an action scene;

'FIG. 2 is a schematic diagram representing an illustrative composite film processing procedure in accordance with the invention;

FIG. 3 is a schematic drawing representing a typical test chart;

FIG. 4 is a schematic drawing representing three illustrative color sepa-ation positive records of the test chart;

FIG. 5 is a schematic drawing representing a color diference mask in accordance with the invention;

FIG. 6 is a schematic drawing repre enting a complete synthetic color separation record in accordance with the invention;

FIG. 7 is a schematic graph representing an illustrative characteristic curve for a color difference mask; and

FIG. 8 is a schematic diagram representing another illustrative composite film processing procedure in accordance with the invention.

As represented schematically in MG. 1, a foreground or action subject 2% is photographed against a uniform backing A camera is indicated illustrativcly as the mo ion picture camera with lens 25 and film 27. Backing 22 typically comprises a screen painted a suitable pure color, which will be taken for illustration as deep blue. The action and backing are illuminated, as by the flood lights 28, with light which is typically White light, and in any case includes an appreciable proportion of light of the backing color. The backing then appears blue, and will be referred to as illuminated with blue light. Auxiliary lights 29, which may be provided with blue 1 lters not shown, may illuminate only the backing. As in blue screen processes of prior art, backing 23 may alternatively comprise, for example, a deep blue translucent screen illum nated from behind.

Film is typically a monop-ack color film which yields on development a color negative, indicated at fit) in FIG. 7.. An illustrative type of film is the well known color negative film manufactured by the Eastman Kodak Company as Eastman Motion Picture Color Negative 5248. z iltei'naatively, camera 24 may, for example, be of the known type that employs one or more beam splitting devices and filters to expose simultaneously a plurality of separate films which on development yield directly respective color separation negative records of the action scene. The action subject 2 3, which may comprise a wide variety of foreground subject matter, is shown schematically in H68. 1 and 2 as asimple sphere.

it has been found helpful, as a guide and check in the laboratory processing operations, to provide in conjunction with each production scene a few frames of a special test chart. A particularly useful form of chart i shown schematically at 27a. in 3.

The present test chart 27a comprises three horizontal rows of square sample areas, of which row A forms a grey scale, shading by definite steps from white at the left to black at the right. For clarity or illustration only five steps are shown in each row, but for actual control of the color process a test chart having eight or more steps in each row is use ul. In row B of chart 27a, white shades into rich, pure blue. Since White comprises an equal mixture of primary colors, the relative blue con tent of row B remains constant from left to right, whereas the green contentand also the red content decrease from unity to zero. In row C white shades into rich yellow. In this case the blue content decreases from unity at the left to zero at the night, the green and red contents remaining constant. The representation of colors in PEG. 3 is necessarily schematic and approximate. Appearance of blue color is represented as horizontal shading, of yellovt as vertical shading. Greys and black are represented by diagonal shading. The rich blue of the chart at square B5, is typically identical with the backing illumination, which in practice normally surrounds the action. That surround is not explicitly shown in FIGS. 3 to 6, but may be considered to be represented by the blue square B5.

Referring now to FIG. 2, illustrative positive color separation records of the action scene are represented as the blue, green and red records 31, .32 and Each positive color separation record is typically made in known manner, as by exposing a black-and-white film to the image of color negative 3d formed in light or" the corresponding color. Such printing, which may, like other printing steps, be by contact or by projection, is indicated by the arrows 4-1, d2 and 43. Thus, the blue record 31 is exposed by blue light transmit-ted by the color negative. A blue object, for example, appears yellow (minus blue) in the color negative; hence blue light incident on that film is not transmitted, and the blue sep- 'aration positive is not exposed at the corresponding area. The developed positive blue record therefore has a very light density at such areas, as in the area of blue backing 22 (FIG. 1). On the other hand, the green and red positive records 32 and 33 are dense in such areas, since the green and red printing light is transmitted by the color negative.

Typical blue, green and red color separation records of test chart 27a are represented schematically at 31a, 32a. and 335a, respectively, in FIG. 4. These records are typically on black and white film and the density variations are indicated by stippling. The grey scale in row A of the test chart appears the same in all t ee color separation records for the reasons already discussed. Rows B and C of green record 32:: are essentially identical with the corresponding rows of red record 33a. That, of course, would not be true of a red or green scale, it they were included in the test chart.

in FIG. 2 a typical color negative of the background scene is indicated schematically at as, with blue, green and red positive color separation records at 61, 62 and 63, respectively. A dense background or male matte is indicated at ill, with a dense black silhouette of the action against a clear field. It is used in printing each of the background separation records to block out the action area. Such a background matte may be prepared in known manner, for example by first making a dupe negative 65 of the green or red positive separation record by the direct printing step as or and then exposing 18. hi h contrast film to light transmitted by blue positive separation record 331 and green negative 65, as indicated by the arrow or. The complementary records 31 and 65 provide density in all parts of the action area, while the background is clear in both recor s. The result is the dense female or action matte as. Direct printll) ing of matte 63, as indicated by the arrow 69, yields the required male or background matte ill.

With background matte 7d superposed successively on background color separation records or, 62 and 63, the color information of the latter is typically transferred to the color dupe negative lltl by successive printing steps til, 52 and $3 with light of the corresponding colors. As illustration, negative $0 may comprise the intermediate color film sold by Eastman Kodak Company as 5253. Before development, color dupe negative must also receive similar information for the action area of the picture.

Since the green and red positive separation records 32 and 33 for the action scene have high density in the area of the backing, as indicated schematically in FIG. 2, those records may be printed satisfactorily in conventional manner without masks or with only light cover masks to produce the green and red action information on the dupe negative of the complete picture. Such printing steps are indicated by the arrows 52 and 53.

In accordance with the present embodiment of the invcntion the green positive separation record 32, or its approximate equivalent, is employed also, together with a compensating mask of novel type, to record the blue information in the action area of the complete picture.

7 Such a compensating or color difference mask is indicated schematically at Sll in PEG. 2, and typical density variations on such a mask for test chart 27a are indicated at dlla in FIG. 5. The arrow 51 in FIG. 2 represents the printing step by which the blue component information is printed on color dupe negative as, not from blue positive separation record 31, but from the synthetic blue record which typically comprises green record 32 and color difference mask 50 in superposition. That printing step must, of course, be carried out with blue light to have the proper effect on the color responsive film 80.

Color difference mask 50 may be produced, in principle, by exposing a film to light the intensity of which at each area corresponds generally to that which was used to expose blue positive record fill minus that used to expose green positive record 32. Thus the color difference mask may be considered to result from two exposure components, one of which is essentially positive and the other essentially negative. The desired differential light image may be obtained, for example, by passing blue light through color negative 36 and green positive record 32 in superposition, as indicated by the arrow as in FIG. 2. In that printing operation the blue light transmitted by the color negative corresponds to that in printing step ll ordinarily employed to make blue record Ill, as already described; and green record 32 removes from that light a proportion corresponding to the green record density at each area, which density represents the green light transmitted by the color negative, as already described for printing step 42. If a special color separation camera is used to photograph the action scene, direct color separation negatives take the place of color negative Sill of FIG. 2, and are merely printed to produce the respective positive color separation records 331, 32 and 33. The color diilerence mask may then be produced by printing with light of any desired color through the blue separation negative and the green separation positive in superposition.

in actual practice, the detailed nature of the color difierence mask is readily controllable in various ways. Its absolute density is controllable by suitable selection of the intensity or duration of the printing exposure. Appreciably more exposure is preferably used than would be required to print the blue record 31 itself, so that some areas that are clear in record 31a of FIG. 4 show appreciable density in mask Ella of PEG. 5. That is especially true of areas in which is clear, for example square Al; but it is not true where green record 32 is dense, as in square B5, for example. A satisfactory color difference mask is ordinarily obtaingreen positive record 32a lll able by use of a film such as that sold by Eastman Kodak Company under the identifying number 5235, developed to the value of gamma that would be used for an ordinarly blue separation record, typically about 0.9.

The relative importance of the two exposure components employed to make the color difference mask may be controlled, for example, by replacing the regular green separation record 32 by a specially prepared green record, he properties of which are appropriately selected for that specific purpose. In preferred form of the invention, that special record, which will be referred to for convenience as the cancellation green separation record, is given sufiicient exposure to maintain even the lightest densities substantially on the straight-line portion of the characteristic curve of the film stock used, thus avoiding the toe region of the curve. Also, the green cancellation record is preferably developed to a lower contrast than is normally used for the regular green record 32. For example, it is ordinarily desirable to employ a film such as that sold by Eastman Kodak Company under the identifying number 5234, exposed to give a minimum density of 0.7 to 1.0 for white objects and developed to a gamma of about 0.65. The precise value of the contrast for any particular set of materials and conditions is preferably selected to give uniform density on the color difference mask 50 for all shades of a grey scale, such as row A of the test chart. if the density of row A of the color diiference mask (EEG. increases toward the right, the cancellation green separation should be developed to higher gamma, and vice versa. Since the cancellation green separation record typically does not differ greatly from the regular green separation record, the former is not separately illustrated.

In the schematic diagram of FIG. 2 it will be noted that green separation record 32 is used for four distinct operations, indicated by arrows 4-6, 51, 52, and 66. Although only one record 32 is explicitly shown, it is to be understood that distinct records may be prepared and used for each of those purposes, or for any groups of them, the detailed characteristics of the respective records, such as average density and contrast, for example, being varied as desired. In particular, it is useful to make a special cancellation green separation record for printing operation 46, as just described. A separate record is also useful for printing step 656, leading ultimately to background matte itl. A single green positive separation record is usually satisfactory for printing both the blue and the green action information, steps 5i and 52, already described; but separate records may be employed for those steps also if desired. The same is true in general for other records that are employed for more than one printing step.

FIG. 6 represents, for the test chart, the combined effective density variations for the combination 54a of green positive separation record 32a and color difference mask 50a in superposition. That c mbination is employed directly, that is, without any dense foreground matte, in printing step 51 of 2, as a substitute for the masked blue separation record used by previous blue screen processes. The densities of substitute combination 54a as shown in FIG. 6, are less than actual sum of the densities of the two superposed records, in order to represent the increased printing exposure that is employed. The substitute combination will be seen to provide relative densities effectively identical with of the regular blue separation record 31a throughout both the grey scale (row A) and the white-yellow scale (row C). Hence all greys from white to black and all shades of yellow are correctly rendered in the final picture, just as if the substitution had not been made. The same is true generally of reds and of mixtures of red and yellow, not explicitly shown in the present test chart.

Further, substitute combination 54a is essentially the san e as regular blue separation record 31:; the first few steps of row B. Hence pastel shades of blue are also 1 o am properly reproduce". The same is true gneerally of all colors that contain nearly as much green as blue. On the other hand, colors containing appreciably more blue than green appear in substitute combination 54a with higher density than in the regular blue record 31a. That effect becomes more marked as the relative blue content increases, as in moving to the right in row B; and reaches an extreme for pure blue, represented by square B5, for which the substitute combination is essentially opaque although the regular blue record 31a is effectively clear. Because of that difference, the areas of substitute combination 54a that correspond to the blue backing 22; of FIG. 1 are substantially opaque, rather than clear as in the re ular blue separation record 31a. Hence the substitute combination can be used directly. to control the blue component of the action area of the complete picture, just as tie regular green and red separation records 32a and 33a are used in any conventional manner to control the green and red components.

As will be described more fully in connection with PEG. 8, the substitute combination represented in FIG. 6 can be prepared as a single film by successively exposing a film to the printing steps represented by arrows 42 and 4-6 in FlG. 2 and then developing.

An important feature of the invention in its present form is the ability of the substitute blue record, represented illustratively at 54a in FIG. 6, to distinguish sharply betweer tnose colors having a slight excess of blue, which are recognized, and those consisting predominantly of blue, which are not recognized. The actual threshold of blue recognition is closely associated with the effective threshold of sensitivity of the film employed to make the color difference mask. That can be seen clearly by comparing the trend of density in row B of blue and green records 31a and 32a in HQ. 4 and of color difference mask 59a in FIG. 5. In green record 32a the density of row B increases to the right. To overcome that trend, as would be necessary to produce the uniform density of blue record 31a, a superposed mask would require a density decreasing to the right at a corresponding rate. That decrease actually appears in the first two squares B1 and B2 of the color difference mask, and produces in combination 54a (FIG. 6) substantially equal density in squares El and B2, as in blue record 310.

However, that density decrease from left to right in row B of the color difference mask is checked abruptly after the first few squares by the simple fact that clear film has been reached and no further density decrease is possible. From that point on toward pure blue, the color difference mask is essentially uniform, and the increasing density of green record 3201 is controlling. The exact point at which that threshold effect occurs can be controlled by suitable selection of the initial density at square El, which is the grey scale density as already explained.

The phenomena just described may perhaps be visualized more clearly from FIG. 7, in which the usual characteristic curve for a typical color difference mask is plotted as the solid line 96. The grey scale density is indicated illustratively at 91, at the beginning of the toe portion of the curve. Blue deficient colors then appear along the straight portion of the characteristic curve, with maximum density, typically indicated at d2, corresponding to pure yellows and greens. Blue excess colors appear below the grey scale density hi. If the curve continued below point 91 in a straight line, as indicated by the broken line 94, such colors would appear along that curve, with pastel blues typica ly at 95 and pure blue at 96, sa Since negative densities do not occur, and the characteristic curve actually bends as indicated, pastel blues appear as at 97 along the toe portion of the curve just below grey scale density 91; and the pure blue of the backing appears at as clear film.

From the above discussion it will be seen that if the grey scale density 91 is shifted far into the toe portion of the characteristic curve of the color difference mask delicate dillferences in off whites may be lost, not only for slightly blue excess colors but even for slightly blue deficient colors. On the other hand, if the grey scale density is placed relatively high up the characteristic curve, for example at a density of 0.7 or somewhat more, as at 9%, a wide range of blues may be Well reproduced, while still maintaining essentially clear film for the pure blue of the backing.

That latter arrangement, however, has the potential practical disadvantage that the blue light transmitted by transparent or partially transparent parts of the action scene is more fully reproduced as blue in the final picture. Such objects therefore tend to take on a blue cast. Such color shading of transparent objects increases with increasing grey scale density.

When smoke or other transparent objects constitute a particularly important part of the action scene, the color shading of such objects can be reduced by reducing the value of the grey scale density. Alternatively, it is sometimes helpful to maintain a normal value of grey scale density, but to raise the density of the difference mask in the backing region only. Normally that area of the difference mask is quite clear. Suitable additional exposure of the dilference mask before development can raise the density of the backing area up to the grey scale density and thus substantially eliminate color shading of transparent objects. By limiting such density increase to regions of substantially pure blue, the i e-exposure has little or no effect on the rendition of colors having only slight excess of blue. Such additional exposure of the color difference mask may precede or follow the main exposure 46 already described. It may be made, for example, with green light through the original color negative 30 and the positive blue separation record 31 in superposition, as represented by the dashed arrow 56 in FIG. 2. In that exposure only areas of strong pure blue, such as that from the backing, will be effectively clear on both films, and therefore a light exposure produces additional density primarily only in the backing area of the color difference mask.

An alternative embodiment of the invention is represented schematically in FIG. 8 and illustrates the wide variety of detailed procedures which are embraced within the scope of the present invention. In the illustrative procedure of FIG. 8 the actual color information of both action and background scenes is handled without use of any regular color separation records as such. The blue information component of the action scene is printed by means of a synthetic blue separation record which corresponds to the substitute combination already described in connection with FIG. 2. The background matte is produced with the aid of blue and minus-blue component records of the action scene.

The initial action and background color negatives 130 and 160 are typically identical with 30 and 6t respectively, of FIG. 2. A positive action record 134 is prepared, as by printing the action color negative 130 to a suitable intermediate color responsive film, such as Eastman Kodak Company 5253, as indicated by the arrow 144, employing a yellow filter. The green and red light passed by such a minus-blue filter produces at 134 a regular positive color record of the action scene, except that the blue component is absent. That record has a substantially black surround, due to the blue illumination of the backing. The green and red action information can be transferred from color positive 134 to the dupe color negative 1% by directly printing film 134 in yellow light to a second intermediate color film, typically of the same kind, as indicated by the arrow 155.

The blue action information is transferred to dupe color negative 186 in accordance with the present form of the invention, by printin a specially prepared synthetic blue separation record 154, using blue light, as indicated by the arrow 151. That synthetic record corresponds generally to the substitute combination already discussed li in connection with FIG. 6; and printing step 151 corresponds generally to step 51 of the procedure of FIG. 2.

Synthetic blue separation record 154 may be produced by two successive printing exposures. One of those exposures indicated at 142', is made in green light through color negative 136 and produces densities equivalent generally to those of green positive separation record 32 of FIG. 2. The other printing exposure, indicated at 146, is made in blue light through color negative and a cancellation green separation record in superposition. The latter is represented at 32 in FIG. 8 and is generally equivalent to the cancellation green record already discussed and shown schematically at 32 in FIG. 2. Hence printing exposure 146 produces in film 154 densities equivalent generally to those produced in color dillerence mask 58 of FIG. 2 by printing step 46. Development of film 1534 after those two exposures 142 and 146 therefore produces in that one film density variations corresponding to those of the combination of green separation record 32 and color difference mask Stl of FIG. 2 in superposition. The printing step ?151 through synthetic blue record 154 to color dupe negative 13%? is thus equivalent to printing through the two films 32 and 55 of FIG. 2 in superposition, and may be described in such terms even though the densities characteristic of the two films actually appear in a single emulsion. The eitect of that printing step 151 on dupe color negative 189 will be fully understood from the discussion already given in connection with RIG. 2.

In the procedure of FIG. 8 the background color information is transferred from background color negative first to a background color positive 164, as by direct printing in white light. Developed color positive 164 is masked with the dense background matte 1'70 and printed in white light to dupe color negative 180, as indicated by the arrow 184.

Background matte 170 may be produced in any suitable manner, for example as described for matte 8i) of FIG. 2. In the present illustrative procedure, a blue positive separation record 131 or the action scene is printed by blue light transmitted through action color negative 130. The exposure and development of record 131 may be freely adapted as desired specifically for matte production since it is not required for other purposes. A complementary record of the action with clear surround is provided at 165, as by exposing a black and White emulsion in printing step R66 to light of suitable color transmitted by the combined green and red action record 134. A specially prepared color record similar to 34 may be employed for that purpose if desired. it is preferred to employ both green and red light for that printing step 166. By thus effectively using both green and red aspects of the action material, the chance is greatly reduced that a clear area will appear in negative record 165 at a part of the action that is also clear in positive record 151. A corresponding effect may be obtained in the illustrative procedure of FIG. 2, as by supplementing printing step 66 by a successive exposure 66a of film 65 made through positive red separation record 33. After development of record 165, it is printed in step 167 in superposition with record 131 to produce the female or action matte 168. Reversal of that image, as by printing step 169, yields the required background matte 1'70.

It is common practice in prior art blue screen processes to print the green and red action separation records, corresponding to steps 52 and 53 of FIG. 2, through relatively light cover mattes, to prevent any veiling of the background area of color dupe negative 80 or its equivalent. Such mattes normally require a density of only about 0.3 or 0.4 when the backing is translucent blue screen illuminated from the rear; and about 0.7, for example,

when an opaque blue painted backing is used. In accordance with the present invention such cover mattes may also be useful, not only with the green and red separation records, but withthe synthetic blue separation record.

Such relatively light cover mattes, however, do not cause the serious color fringes at the boundaries between action and background areas, avoidance of which is an important advantage of the invention.

The illustrative processes thus far described have provided a synthetic blue separation record based fundamentally on the green separation record, that is to say, on the record for the wavelength region immediately adjacent the region of the backing illumination, which has been taken as blue for illustration. Whereas that choice of a substitute record has been found to afford some practical advantages, it is sometimes preferable, instead, to base the synthetic separation record on the record for a wavelength region that is spaced from the region of the backing illumination. For example, in a blue screen process the synthetic blue record may be based on the red wavelength region. The synthetic blue separation record then typically comprises the red separation positive record and a color difference mask that compensates partially for the density differences between red and blue records. Such a color difference mask can be prepared in a manner corresponding to that already described in connection with printing step 46 of FIG. 2, for example, but employing red record 33 in place of green record 32.

One advantage in thus basing the synthetic blue record on the red separation record is that the background area of the latter is typically more reliably and uniformly dense than that of the green separation record. That is particularly true in the important case that the backing 22 (FIG. 1) comprises an opaque screen painted with the selected color. Such a painted backing has the known advantage that it can be brought forward under the feet of actors, permitting certain types of composite scene that are virtually impossible with a translucent backing. On the other hand, the pigments available for painting an opaque backing generally produce colors of limited purity. In particular, blue paints are found to reflect an appreciable amount of light in the directly adjacent green region of the spectrum. Also, the effective spectral sensitivity of the emulsions and filters normally employed for reparing a green separation record typically exhibit a toe portion in the blue wavelength region. For both of those reasons the green separation positive record 32 tends to have a surround that is not as dense as might be desired, sometimes requiring strengthening by a light cover matte, as already described. However, even a painted blue backing typically reflects very little red light, so that the red separation positive 33 ordinarily has a background area of satisfactory density. By basing the synthetic blue separation positive on the record for the non-adjacent red region, the clean printing quality of its background area is carried over to the blue printing step.

in accordance with a further aspect of the invention, the regular color separation record for one of the wavelength regions other than that of the backing illumination may be replaced by the combination of a color separation record for another such region and a suitable color difference mask. It is particularly helpful to replace the color separation record for the wavelength region adjacent the region of the backing illumination by a synthetic separation record based on a region spaced from the backing illumination. in a blue screen process that aspect of the invention illustratively comprises deriving green action information for the composite picture from the red separation record and a suitable color difference mask.

1G. 9 represents the pertinent portions of an illustrative embodiment of the invention utilizing a positive red separation record as the basis for supplying to the composite picture all three color components of-the action scene. The background scene may be supplied to the color dupe negative 239 via the printing step 184. That step is typically like step 184 of FIG. 8, or the three steps 81, 82 and 33 of FIG. 2, and requires no further description.

Red positive record 33 of FIG. 9 is typically produced by printing step 43, whereby the action color negative 3% is printed in red light to a black and white emulsion, as in FIG. 2. The blue color difference mask 250 is then typically printed at 246 in blue light transmitted by color negative 3i? and red record 33 in superposition; and the green color diiierence mask 252 is similarly printed at 242 in green light transmitted by color negative 3%) and red record 33 in superposition.

The red action information is supplied to color dupe negative 2% by direct printing 53 of red record 33 in red light, as in FIG. 2; the blue action information by printing in blue light red record 33 and blue color dif ference mask 25b in superposition, as at 251; and the green action information by printing in green light red record 33 and green color difference mask 252 in superposition, as at 254.

Although all of the printing steps 242, 246, 251, 253, and 254 are represented for clarity in FIG. 9 as utilizing the same red positive separation record 33, separate records may be prepared for some or all of those steps, the detailed nature of the several records being varied in any desired manner to suit the particular purposes for which they are intended.

In preparing blue color difference mask 250 the value of the grey scale density is subject to restrictions corresponding to those already described for color difference mask 5%) of FIG. 2, for example. But the denser background region of red record 33 typically permits a somewhat higher value of the grey scale density. On the other hand, green color difference mask 252 is substantially free of such restrictions. Hence the latter mask may be given a grey scale density hi h enough to produce eliectively complete color compensation of the action scene for most green excess colors (relative to red, of course), as well as for green deficient colors, without appreciably lightening the desirable dense surround that is characteristic of the red record, and without degrading the color of transparent objects.

It will be understood by those skilled in the art that the particulars of the procedures that have been described for illustration may be varied in many different ways without departing from the spirit and true scope of the invention. In particular, the invention in its broader aspects is not necessarily limited to selection of any particu ar color for the background illumination. Whereas blue background illumination has been found to be re markably advantageous for photographing most normal action scenes, it will be evident from the description that the invention can be modified to employ a red backing, for example, for photographing special action scenes in which blues predominate and reds are substantially absent. Moreover, it is well known in photography that positive and negative records are in many respects interchangeable, and that many types of emulsion can be developed by reversal processes to yield a positive image directly. Application of such known equivalents regularly lead to a wide variety of possible alternative procedures, detailed description of which is believed unnecessary for a clear understanding of the invention.

I claim:

1. In a blue screen process for making a composite color photograph, which process comprises making a photographic color record of a background scene, making a photographic color record of a foreground scene before a backing illuminated by substantially pure blue light, and transferring color information from said records to respective background and foreground areas of a composite color record to produce a complete color picture; the improvement which comprises producing from the color record of the foreground scene a positive color separation record for a Wavelength region other than blue, producing from the color record of the foreground scene a light image in which the light intensities correspond inversely to the blue color component of the foreground scene, removing from said image light intensities corresponding to the density variations of said positive color separation record, exposing an actinic layer to the resulting light image and developing the exposed layer to produce a color difference mask, and utilizing a color separation record for said wavelength region other than blue and said color difference mask in superposition as a blue color separation record in producing said composite color record.

2. The improvement defined in claim 1, and wherein said exposure of the actinic layer is sufficient to produce only a selected limited density less than about 0.7 in the developed layer at areas corresponding to White objects of the foreground scene.

3. In a blue screen process for making a composite color photograph, the method of printing the blue component of the foreground scene, said method comprising in combination the steps of producing a photographic color record of a foreground scene before a backing illuminated by blue light, producing from the color record a green color separation positive having a dense background area corresponding to the blue backing illumination, producing from the color record a color difference mask having substantially zero density in areas corresponding to colors consisting predominantly of blue, and having in areas corresponding to other colors, densities that correspond essentially to the densities of a blue color separation positive minus the densities of a green color separation positive, and printing the blue component of the foreground scene by exposure through the green color separation positive and the color difference mask in superposition, the dense background area of the latter positive acting as a foreground matte during said exposure.

4. A process as defined in claim 1, and wherein said wavelength region other than blue is the green region and the magnitude of said exposure of the actinic layer is se lected in direct relation to the ratio of blue to green content in the colors to be reproduced.

5. A process as defined in claim 1, and wherein said positive color separation record is developed to a value of gamma for which the color difference mask has substantially the same density for all grey scale objects of the foreground scene.

6. The process for making a composite color photograph, which process comprises making a photographic record of a background scene, making a photographic color record of a foreground scene before a backing illuminated by light confined substantially to a first wavelength region of the visible spectrum, producing photographicaily from the color record of the foreground scene a color separation positive for a second Wavelength region of the visible spectrum which substantially excludes said first region, the background area of said positive being dense by virtue of the substantial absence from the backing illumination of light from said second wavelength region, producing photographically from the color record of the foreground scene a color difference mask having densities at its respective foreground areas that correspond essentially to the densities of a color separation positive for the first wavelength region minus the densities of a color separation positive for the second wavelength region, the background area of the color difference mask being essentially clear, printing the color component of the foreground scene corresponding to the first Wavelength region by exposure through the color separation positive for the second wavelength region and the color difference mask in superposition, the dense background area of that positive acting as a foreground matte during said exposure, printing the color component of the foreground scene corresponding to the second wavelength region, producing a dense background matte, and printing the background scene by exposure through the photograhic record of the background scene and the background matte in superposition.

7. The process defined in claim 6, and wherein the first mentioned color separation positive and the color difference mask are produced in a common emulsion layer.

8. The process defined in claim 6, and wherein the color difference mask is produced by exposing an actinic layer to light of said first Wavelength region transmitted by a negative muIti-color record of the foreground scene and by a color separation positive of the foreground scene for said second Wavelength region in superposition, and developing the actinic layer.

9. The process defined in claim 6, and wherein said second wavelength region is spaced from said first wavelength region.

10. The process for making a composite color photograph, which process comprises making a photographic record of a background scene, making a photographic color record of a foreground scene before a backing illuminated by substantially pure blue light, producing photographically from the color record of the foreground scene a green color separation positive having a dense back ground area corresponding to the blue backing illumination, producing photographically from the color record of the foreground scene a color difference mask having densities at its respective foreground areas that correspond essentially to the densities of a blue color separation positive minus the densities of a green color separation positive, the background area of the color difference mask being essentially clear, printing the blue component of the foreground scene by exposure through the green color separation positive and the color difference mask in superposition, the dense background area of said green positive acting as a foreground matte during said exposure, printing the components of the foreground scene other than blue, producing a dense background matte, and printing the background scene by exposure through the photographic record of the background scene and the background matte in superposition.

11. The process defined in claim 10, and wherein the color differencemask is produced by exposing an actinic layer to blue light transmitted by a negative multi-color record of the foreground scene and by a green color separation positive of the foreground scene in superposition, and developing the actinic layer.

12. The process defined in claim 11, and wherein the exposure of said actinic layer is selected to give a predetermined density value in areas corresponding to white objects of the foreground scene.

13. The process defined in claim 12, and wherein said predetermined density value is less than about 0.7.

14. In a blue screen process for making a composite color photograph, the method of printing the blue component of the foreground scene, said method comprising in combination the steps of producing a photographic negative multi-color record of a foreground scene before a backing illuminated by blue light, producing from the color record a first green color separation positive exposed and developed to have substantially normal density and contrast and having a dense background area corresponding to the blue backing illumination, producing from the color record a second green color separation positive exposed and developed to have a density of at least about 0.7 for white objects and a gamma of approximately O.65,exposing an actinic layer to blue light transmitted by the negative multi-color record and the second green color separation positive in superposition and developing the actinic layer to produce a color difference mask, and printing the blue component of the foreground scene by exposure through the first green color separation positive and the color difference mask in superposition, the dense background area of the latter positive acting as a foreground matte during the last said exposure.

15. The process for making a composite color photograph without using a dense foreground matte, which process comprises making a photographic record of a background scene, making a photographic multi-color negative record of a foreground scene illuminated by essentially white light before a backing illuminated by substantially pure blue light, producing from the negative record a red color separation positive and at least one green color separation positive having dense background areas corresponding to the blue backing illumination, exposing an actinic layer to blue light transmitted through the negative record and a green color separation positive in superposition and developing the actinic layer to produce a color difference mask having densities at its respective foreground areas that correspond essentially to the densities of a blue color separation positive minus the densities of a green color separation positive, the background area of the color difference mask being essentially clear, printing the blue component of the foreground scene by exposure through a green color sepation positive and the color difference mask in superposition, the dense background area of that green separation positive acting as a foreground matte during such exposure, printing the green and red color components of the foreground scene by exposure through respective green and red color separation positives, the dense background areas thereof acting as foreground mattes during such printing, producing a dense background matte, and printing the background scene by exposure through the photographic record of the background scene and the background matte in superposition.

16. The process for making a composite color photograph Without using a dense foreground matte, which process comprises making a photographic record of a background scene, making respective red, green and blue color separation negatives of a foreground scene illuminated by essentially white light before a backing illuminated by substantially pure blue light, producing from the green and red negatives respective green and red color separation positives having dense background areas corresponding to the blue backing illumination, exposing an actinic layer to light transmitted through the blue negative and a green positive in superposition and developing the actinic layer to produce a color difference mask having densities at its respective foreground areas that correspond essentially to the densities of a blue color separation positive minus the densities of a green color separation positive, the background .area of the color difference mask being essentially clear, printing the blue component of the foreground scene by exposure through a green color separation positive and the color difference mask in superposition, the dense background area of that green separation positive acting as a foreground matte during such exposure, printing the green and red color components of the foreground scene by exposure through respective green and red color separation positives, the dense background areas thereof acting as foreground mattes during such printing, producing a dense background matte, and printing the background scene by exposure through the photographic record of the background scene and the background matte in superposition.

17. The process for making a composite color photograph Without using a dense foreground matte, which process comprises making a photographic record of a background scene, making a photographic inulti-color negative record of a foreground scene illuminated by essentially White light before a backing illuminated by substantially pure blue light, producing from the negative record at least one green color separation positive having a dense background area corresponding to the blue backing illumination, producing from the negative record a color positive containing the green and red components of the foreground scene and having a dense background area corresponding to the blue backing illumination, exposing an actinic layer to blue light transmitted through the negative record and a green color separation positive in superposition and developing the actinic layer to produce a color difference mask having densities at its respective foreground areas that correspond essentially to the densities of a blue color separation positive minus the densities of a green color separation positive, the background area of the color difference mask being essentially clear, printing the blue component of the foreground scene by exposure through a green color separation positive and the color difference mask in superposition, the dense background area of that green separation positive acting as a foreground matte during such exposure, printing the green and red color components of the foreground scene by exposure through the green and red color separation positive, the dense background area thereof acting as a foreground matte during such printing, producing a dense background matte, and printing the background scene by exposure through the photographic record of the background scene and the background matte in superposition.

18. The process for making a composite color photograph without using a dense foreground matte, which process comprises making a photographic record of a background scene, making a photographic multi-color negative record of a foreground scene illuminated by essentially white light before a backing illuminated by substantially pure blue light, producing from the negative record at least one red color separation positive having a dense background area corresponding to the blue backing illumination, exposing an actinic layer to blue light transmitted through the negative record and a red color separation positive in superposition and developing the actininc layer to produce a blue color difierence mask having densities at its respective foreground areas that correspond essentially to the densities of a blue color separation positive minus the densities of a red color separaton positive, exposing a second actinic layer to green light transmitted through the negative record and a red color separation positive in superposition and developing the second actinic layer to produce a green color difference mask having densities at its respective foreground areas that correspond essentially to the densities of a green color separation positive minus the densities of a red color separation positive, the background areas of the color difference masks being essentially clear, printing the blue and green components of the foreground scene by respective exposures through a red color separation positive and the blue color difference masks in superposition and through a red color separation positive and the green color difference mask in superposition, the dense background area of the red separation positive acting as a foreground matte during such exposures, printing the red color component of the foreground scene by exposure through a red color separation positive, the dense background area thereof acting as a foreground matte during such printing, producing a dense background matte, and printing the background scene by exposure through the photographic record of the background scene and the background matte in superposition.

19. The process for making a composite color photograph without using a dense foreground matte, which process comprises making a photographic record of a background scene, making a photographic multi-color negative record of a foreground scene illuminated by essentially white light before a backing illuminated by substantially pure blue light, producing from the negative record a red color separation positive and at least one green color separation positive having dense background areas corresponding to the blue backing illumination, exposing an actinic layer to blue light transmitted through the negative record and a green color separation positive in superposition, exposing said actinic layer to green light transmitted through the negative record, said exposures being in registration, developing the actinic layer to produce a synthetic blue separation positive having densities at its respective foreground areas that correspond essentially to the densities of a blue color separation positive, and having a dense background area by virtue of said exposure to green light, printing the blue component of the foreground scene by exposure through the synthetic blue color separation positive, the dense background area thereof acting as a foreground matte during such exposure, printing the green and red color components of the foreground scene by exposure through respective green and red color separation positives, the dense background areas thereof acting as foreground mattes during such printing, producing a dense background matte, and printing the background scene by exposure through the photogr-auhic record of the background scene and the background matte in superposition.

References Cited in the file of this patent UNITED STATES PATENTS Hyde July 31, 1906 Wilkinson Nov. 23, 1937 Oliver Mar. 24,1942 Gaspar Oct. 30, 1945 P0111 Nov. 2, 1954 Weir Feb. 20, 1962 

16. THE PROCESS FOR MAKING A COMPOSITE COLOR PHOTOGRAPH WITHOUT USING A DENSE FOREGROUND MATTE, WHICH PROCESS COMPRISES MAKING A PHOTOGRAPHIC RECORD OF A BACKGROUND SCENE, MAKING RESPECTIVE RED, GREEN AND BLUE COLOR SEPARATION NEGATIVES OF A FOREGROUND SCENE ILLUMINATED BY ESSENTIALLY WHITE LIGHT BEFORE A BACKING ILLUMINATED BY SUBSTANTIALLY PURE BLUE LIGHT, PRODUCING FROM THE GREEN AND RED NEGATIVES RESPECTIVE GREEN AND RED COLOR SEPARATION POSITIVES HAVING DENSE BACKGROUND AREAS CORRESPONDING TO THE BLUE BACKING ILLUMINATION, EXPOSING AN ACTINIC LAYER TO LIGHT TRANSMITTED THROUGH THE BLUE NEGATIVE AND A GREEN POSITIVE IN SUPERPOSITION AND DEVELOPING THE ACTINIC LAYER TO PRODUCE A COLOR DIFFERENCE MASK HAVING DENSITIES AT ITS RESPECTIVE FOREGROUND AREAS THAT CORRESPOND ESSENTIALLY TO THE DENSITIES OF A BLUE COLOR SEPARATION POSITIVE MINUS THE DENSITIES OF A GREEN COLOR SEPARATION POSITIVE, THE BACKGROUND AREA OF THE COLOR DIFFERENCE MASK BEING ESSENTIALLY CLEAR, PRINTING THE BLUE COMPONENT OF THE FOREGROUND SCENE BY EXPOSURE THROUGH A GREEN COLOR SEPARATION POSITIVE AND THE COLOR DIFFERENCE MASK IN SUPERPOSITION, THE DENSE BACKGROUND AREA OF THAT GREEN SEPARATION POSITIVE ACTING AS A FOREGROUND MATTE DURING SUCH EXPOSURE, PRINTING THE GREEN AND RED COLOR COMPONENTS OF THE FOREGROUND SCENE BY EXPOSURE THROUGH RESPECTIVE GREEN AND RED COLOR SEPARATION POSITIVES, THE DENSE BACKGROUND AREAS THEREOF ACTING AS FOREGROUND MATTES DURING SUCH PRINTING, PRODUCING A DENSE BACKGROUND MATTE, AND PRINTING THE BACKGROUND SCENE BY EXPOSURE THROUGH THE PHOTOGRAPHIC RECORD OF THE BACKGROUND SCENE AND THE BACKGROUND MATTE IN SUPERPOSITION. 